The invention relates to active adaptive control systems, and more particularly to an improvement for limiting output power to prevent overdriving of the output transducer.
The invention arose during continuing development efforts relating to the subject matter of U.S. Pat. No. 5,278,913, and co-pending U.S. application Ser. No. 08/166,698, filed Dec. 14, 1993, incorporated herein by reference.
Active acoustic attenuation involves injecting a canceling acoustic wave to destructively interfere with and cancel an input acoustic wave. In an active acoustic attenuation system, the output acoustic wave is sensed with an error transducer, such as a microphone or an accelerometer, which supplies an error signal to an adaptive filter control model which in turn supplies a correction signal to a canceling output transducer or actuator, such as a loudspeaker or a shaker, which injects an acoustic wave to destructively interfere with the input acoustic wave and cancel or reduce same such that the output acoustic wave at the error transducer is zero or some other desired value.
An active adaptive control system minimizes an error signal by introducing a control signal from an output transducer to combine with the system input signal and yield a system output signal. The system output signal is sensed with an error transducer providing the error signal. An adaptive filter model has a model input from a reference signal correlated with the system input signal, an error input from the error signal, and outputs a correction signal to the output transducer to introduce a control signal matching the system input signal, to minimize the error signal. The filter coefficients are updated according to a weight update signal which is the product of the reference signal and the error signal.
The present invention is applicable to active adaptive control systems, including active acoustic attenuation systems.
The present invention addresses the problem of overdriving of the output transducer. Active control solutions sometimes require more actuator power than is available or desirable. Actuators, amplifiers, etc. have limitations that adversely affect control algorithms. Pushed beyond capacity, the control output or power available from the secondary source or output transducer may exhibit saturation, clipping, or otherwise nonlinear behavior. Excessive control effort can result in damaged actuators, excessive power consumption, and instability in the control algorithm.
It is known in the prior art to provide weight update signal leakage to counteract the adaptive process. This is done by implementing an exponential decay of the filter coefficients, intentionally defeating control effort, Widrow and Stearns, Adaptive Signal Processing, Prentice-Hall, Inc., Engelwood Cliffs, N.J., 1984, pages 376-378. The exponential decay is typically selected to be slow such that the adaptive process toward a control solution dominates. A deficiency of this method is that it unilaterally, across all power levels, degrades performance. Such leakage is useful for limiting control effort and enhancing numerical stability, but performance suffers because of the lack of consideration for regions where the control effort is in an acceptable range. The present invention addresses and solves this problem.